Dynamic force attenuator for a mortar



March 24, 1970 R. F. WINSEN ET AL, 3,501,997

DYNAMIC FORCE ATTENUATOR FOR A MORTAR Filed March 2l, 1968 [Wl ,H mgm//1,7/ o ,/Z 7/ m /Z//i l l l 25% "Wg 74 26 AJ/ 34 F/G. Z P05597 E W//Vswtates ice DYNAMIC FORCE ATTENUATOR FOR A MORTAR Robert F. Winsen, OakPark, and Eugene C. Molnar,

Warren, Mich., assignors to the United States of America as representedby the Secretary of the Army Filed Mar. 21, 1968, Ser. No. 714,868 Int.Cl. Falt 19/06 U.S. Cl. 89-44 3 Claims ABSTRACT OF THE DESCLOSURE Amortar which utilizes an attenuating mechanism to sharply reduce thepeak impact force of recoil. A volumetrically compressible materialwhich surrounds the mortar tube absorbs the recoil force resulting in asubstantially reduced counter-recoil force. The attenuating material iscompressed against a housing by a compressing means which is connectedto the tube.

The invention described herein may be manufactured, used and licensed byor for the Government for governmental purposes without payment to us ofany royalty thereon.

This invention relates to mortars. More particularly this inventionrelates to energy absorbing devices utilized in mortars.

Conventionally, mortars have been utilized as ground based weapons. Muchof the terrain in which mortars are utilized is composed of extremelysoft soil. Repeated tiring of a mortar in this loose or soft soil willcause the weapon to bury itself. For this reason, plus the desire forincreased mobility, the mortar is desirably mounted on a vehicle. Thevehicle thus provides a base of a much larger area and will thereforeeliminate the problem f the mortar sinking into the ground.Additionally, the vehicle provides a means of increasing mobility.

Mounting the mortar in this fashion, however, has given rise toattending problems. If the mortar is mounted on the truck and no recoilmechanism is used to absorb the shock, in a relatively short time, thevehicle structure will deteriorate to an unacceptable level. This is dueto the great impact of the recoil force which must be absorbed entirelyby the vehicle structure as a peak load rather than a distributed load.To distribute this load, conventional recoil mechanisms have beenutilized. In this environment, however, their use has generated furtherproblems. Generally, these recoil systems are effective in keeping thevehicle structure from becoming decadent, however, the counter-recoilforce inherent in this type of system is suiiiciently large to dismantlethe mortar from the vehicle. Obviously, this type of system isunacceptable.

One of the devices utilized in the past to attenuate the force hasemployed a hydraulic shock absorber such as that disclosed in U.S.Patent No. 2,790,357. This type of device has proved unacceptable forseveral reasons among which include the fact that it is expensive,complex, and diicult to maintain.

Other devices which have been utilized in an attempt to attenuate forcehave included both the use of spring devices and expanding rings. Bothof these devices have many disadvantages, the most serious of which isthe fact that tremendous oscillations are set up in the system after theinitial cushioning force, hence the dampening is not quickly effected. Adevice which has radially expanding rings to absorb the recoil energymay be seen in U.S. Patent No. 3,115,063. This device, however, does notoperate on a principle of compression, but rather that of radialexpanison, and hence is quite dissimilar to the instant invention.

lt is one of the objects of the invention therefore to eliminate theaforementioned disadvantages of the prior art systems.

Another object of the present invention is to enable a mortar to betired from a vehicle.

It is another object of the present invention to provide a new andimproved means of absorbing the recoil shock of a mortar.

It is yet another object of the present invention to provide a means forattenuating force that exists in a mortar system and means for securingthe mortar to a vehicle.

A further object of the present invention is to substantially reduce thepeak force transmitted to the vehicle which results from recoil of amortar mounted thereon.

It is av still further object of the present invention to attenuate therecoil and counter-recoil force of a mortar by means of a compressiblematerial mounted about the mortar.

Other objects and advantages of the present invention will becomeapparent to those of ordinary skill in the art by the followingdescription when considered in relation to the accompanying drawing ofwhich:

FIGURE l is an elevational side view of the mortar as it is mounted onthe vehicle according to the invention.

FIGURE 2 is a cross-sectional View of the mortar incorporating theenergy attenuating device according to the invention.

Briefly, in accordance with the invention, it has been discovered thatthe force transmitted by the tiring of a mortar can be greatlyattenuated by the use of acompressible material which surrounds themortar tube. When the mortar is tired, the recoil source is transmittedfrom the mortar tube to layers of compressible material which exhibits arelatively soft response. These layers provide excellent cushioning andvibration damping whereby a large proportion of the recoil force isattenuated by the compressible structure. On counter-recoil, only a verylow percentage of the initial recoil force will remain. Oncounter-recoil, additional layers of material which surround anotherportion of the mortar tube attenuate a similar percentage of theremaining force. The use of the material around the mortar tube willquickly attenuate the shock load and hence will permit the mortar to bemounted on a vehicle without impairing the vehicle structure.

Referring now to the drawing, wherein similar numerals will refer tosimilar parts in the various iigures, a mortar is shown as being mountedon a vehicle bed. As is well known, a mortar is a muzzle loading cannonhaving a short tube in relation to its caliber that is used to throwprojectiles with low muzzle velocities and at high angles. This shortmortar tube in which the projectile is placed is shown at 10. Mortartube 10 is mounted within a hollow piston rod 12, a portion of which isshown is shown at 14. Hollow tubular member 12 is mounted within ahollow cylinder 16, having slots 18 cut therein for improvingventilation and reducing mount weight.

The opposite end of tubular member 12 can be seen extending out theopposite end of the cylindrical support member 16 as shown at 20. Aflange 22 is also formed on either end of support member 16.

A tubular end receiving member 24 is secured to the lower end of supportmember 16 and is adapted to receive portion 20 of tubular member 12. Ascan be seen in the drawing, ventilation slots 26 are cut therein toimprove air circulation, reduce weight and process access to spring pin71. At the lower end of end receiving member 24, a rear mount is showngenerally at 2S. A bushing 30 which may be integrally formed with endreceiving piece 24 is rotatively mounted on trunnion pin 32 whichextends through apertures formed in clevis type receptacle 34. Theclevis type receptacle 34 is attached to base plate 36 and mountingplate 40. The relatively complex rear mount structure 28 could bereplaced by a relatively simple ball and socket wherein the ball isattached to tubular end receivingy member 24 and the socket is attachedto the base. This would enable the mortar to rotate freely about thebase. Bolts 42 are provided to secure base plate 36, base assembly 38,and mounting plate 40.

Intermediate to flanges 22 mounted at opposite end of support housing 16an equilibrator 44 is rotatively mounted in slot 46. The opposite end issuitably journaled on trunnion bearing 4S, which provides the lowermounting means therefore. A spring is mounted within equilibrator 44which tends to hold hollow cylinder 16 in the upright position as shownin the drawing.

An attitude and altitude positioning device is shown generally at 50 andmay generally be composed of either a bifurcated single assembly or twoindividual legs which are spread in opposite direction from a commonpoint adjacent the mortar housing. The two legs in conjunction with themortar tube and its associated tubular end receiving member form atri-pod supporting structure.

A course altitude adjustment device is attached to altitude positioningdevice 50 as shown at 62. A crank as shown at 52 is provided on base 50to adjust the altitude of the mortar tube. A similar lateral positioningdevice (not shown) is also provided with the supporting structure toobtain correct lateral position. Adjustment of altitude position devices50 and 54 causes the mortar tube to rotate about trunnion pins 58 and60, which are secured in an adapted plate 56. Plate 56 may be attachedto cylindrical supporting member 16 in any suitable mechanical mannersuch as by welding.

The particular details of the supporting system are not peculiar to noran important part of the invention. Any other suitable supportingstructure by which the altitude and lateral position of the mortar tubecan be controlled will suffice.

Referring now to FIGURE 2, the mortar tube is connected to tubularmember 12 in the areas designated generally as 64 and 66. Mortar tube 10may be threadedly engaged to tubular member 12 or secured in any othersuitable manner. For instance, a set screw 68 may be utilized to securethe two tubular assemblies.

At the end of mortar tube 10 a spherical ball 70 is shown. Ball 70 isused to adapt the mortar for a direct connection to a vehicle withoutthe use of the mounting assembly according to the present invention.Shown generally at 71 is the conventional ring pin mechanism utilized toinitiate firing of the mortar. It desired, of course, the threads asshown at 64, and set screws as shown at 68 may be eliminated in favor ofa connecting system whereby the ball 70 is connected directly to tubularmember 12.

Intermediate the oppositely disposed ends of tubular member 12, a ring72 is rigidly attached thereto. Ring 72 may be formed as an integralpart of tubular member 12 as shown, or may be individually formed andsubsequently attached by any mechanical, suitable means such as bywelding. The outside diameter of ring 72 should enable the clearancebetween cylindrical housing 16 and rod 12. Mounted on the opposite endsof cylindrical support member 16 are end pieces indicated generally at76 and 78. End piece '76 is securely fastened to cylindrical housing 16by any suitable manner such as pinning. A bushing 74 is secured to endpiece 76 and is engaged with tubular member 12 which is movable relativethereto. End piece 78 is secured to cylindrical housing 16 and is shownas being formed as an integral part of end receiving member 24.Obviously, end member 7S could be formed individually and secured tomember 24 in any other suitable mechanical manner. As shown, a bushing74 is secured to end member 7S, and is adapted to receive tubular member12, which slides back and forth relative thereto.

Secured about tubular member are a plurality of rings of cushioning orattenuating material shown generally at 80 and 82. Rings Si) encirclethe lower portion of tubular member 12 and are mounted intermediate ring72 and end piece 7S. Rings S2 similarly surround tubular member 12 andare positioned intermediate rings 72 and the opposite end piece 76. Theinside diameter of rings should be just large enough to enable them toslide easily over the tubular member 12. The material utilized for rings80 and 82 is one having excellent energy absorbing characteristics whichmakes it an excellent vibration damper at both high and low frequency.The counter-recoil force of a mortar, utilizing this type of material,is very low compared to the recoil force. For example, empirical testshave shown that a 12,000 pound counter-recoil force resulted from asystem utilized initially at 80,000 pounds of recoil force. Thisreduction in force cannot be obtained with a system such as a coilspring, but requires a material which exhibits a very soft response,which cushions the shock and reduces the vibration damping. The materialutilized is a micro-cellular urethane elastomer which was developed forheavy duty mechanical applications. This material provides theadvantages of a cellular product with the additional properties of solidcast elastomers. One of the many advantages of this micro-cellularstructure is its linear deformation, wherein the material will detlectproportionally to the load until the deflection reaches approximately 40to 50% of the total height of the material. ln contrast to materialssuch as rubber, which are noncompressible, this material has theadditional advantage of being compressible.

A material which will meet the requirement of the above described systemin known as Celasto.

Celasto exhibits a combination of open and closed cells predominantlyopen. This material is volumetrically compressible. This material shouldnot be confused with the very low density urethane foams used forpadding and seat cushions. Even if totally confined, Celasto can becompressed to less than one-fourth its original height. Due to itscellular nature, it is possible to compress Celasto springs to a smallfraction of their free length with very little change in diameter. Thisis of peculiar importance where there are space limitations.

In contrast to the cellular elastomeric substance which is utilized inthe present invention, solid elastomers have a common limitation orbeing incompressible. If squeezed in one direction, they must expandproportionally in another; hence, they otfer no spring action whenconfined.

A urethane elastomer which is suited for this purpose has a speciiicgravity of 0.45 and weighs 0.45 gram per cubic centimeter or 28 poundsper cubic foot. The various grades of material may vary from 20 to 40pounds per cubic foot or 0.3 to 0.6 gram per cubic centimeter.

The attenuating rings S0 maintain the tubular member 12 in the positionshown in the drawing under rio-load conditions. The two masses ofattenuating material, such as Celasto, are maintained in position witheither a light or a preloaded pressure, due to the manner of assemblingthe end pieces, the cellular structure and the tubular support member12. The hollow cores 83, formed in each of rings 80 and 82, are alignedwith the openings of the bushings 74, attached to opposite ends of thehollow cylinder 16. The piston rod or tubular member 12 extends throughthe cores of the cushioning material and the bushings 74. The piston rodor tubular member 12 is of suicient length to maintain Contact with thefull bearing surface of bushings 74, at maximum displacement in eitherdirection of the piston rod. The inside diameter of the respective ringsshould be just large enough to enable them to slide easily over thetubular member 12.

The mortar is suitably aligned by means of positioning means 50 and S4.The mortar rotates about its mounts 2,8, 4S, etc., until it is alignedin the desired position. The projectile is inserted in the mortar tubeand tired. The force is applied to the load receiving part of mortartube 10, and is transmitted to the tubular piston 12. The energy istransmitted through ring 72 as the piston is forced backwards againstthe cushioning material 80, compressing it against the end piece 78,until the energy of the impact has been dissipated.

As the tubular piston 12 moves rearwardly toward end piece 78, it slidesthrough the cores 83 of the attenuating material 80 and through thebushing 74. Due to compression of the cellular structure, a part of theimpact energy is absorbed and a part is dissipated. Obviously, a portionof the force is transmitted through the rear mount and into the basestructure. However, the force transmitted to the base structure isreduced because of the energy dissipated by the cushion. When the energyof the impact has been dissipated, the cellular structure rebounds,pushing the piston 12 back towards a neutral position, but with adrastically reduced force. When the neutral position is reached, thepiston is traveling at its highest velocity and its momentum carries itforward past the neutral position. Ring 72 now begins to compress ringsof the attenuating material 82. Because of the reduced force of thecounter-recoil, the number of rings 82 may be less than that of rings80.

The process of energy dissipated and force reduction are now repeatedwith a reduced force being transmitted to the base structure, but in theopposite direction as previously described. The mortar tube againrebounds with the force still further reduced and the piston is pushedback through the neutral position to complete one cycle. This cycle isrepeated through a short series of rapid oscillations of decreasingamplitude until the force is reduced to zero. The piston will then havereturned to the neutral position where it will be prepared to receivethe next impact load, thus repeating the cycle.

Although the system has been shown and described with an assortment ofvarious pieces, it is to be understood that the force may be furtherattenuated by the addition of mass to the recoiling parts, which willcause energy to be consumed in accelerating this mass.

It should be further understood that force attenuation may also beaccomplished by embodying concepts of this invention in a configurationof piston and cushioning masses 80 and 82 which are external to the loadreceiving part. This configuration would permit the arrangement of oneor more pistons about the periphery of the lower receiving part and isaccomplished by containing the piston, cushioning material, andsupporting plate in an assembly supported by the base structure.

In this event each piston would receive the load from the load receivingpart through an arm attached to the end of one of the piston rods.

Another modification of the present invention provides for the assemblyof supporting plates and end pieces, designated above as 78, andcushioning material 80 and 82 to be connected to the load receivingparts such as 10. In this modification the piston or tubular member 12is supported rigidly by the base structure. The force of recoil istransmitted from the motor tube to the supporting plate, which movesforward, thus compressing the cushioning material against the stationarypiston 12. The relative motion of the parts, the oscillating movements,and the disposition of energy and force is the same, in principle, asthe basic invention herein above described.

Although each mass of attenuating material has been described as beingcomposed of a single layer comprised of rings of material disposed inaxially abutting relation, it should be understood that additionalconcentric layers of rings may also be utilized. Moreover, the pluralityof axially abutting rings could be replaced by a single ring if desired.

It should be further understood that to eliminate binding of the disksagainst the rings and against each other, the cushioning material may beassembled with a stiff Washer, such as one composed of steel which islocated between each disk. The inside diameter of the washers placedintermediate the rings of the material should be just large enough toenable the washers to slide easily over the piston rod. The outsidediameter should be a little larger than the outside diameter of thecushioning material so as to maintain separation of the rings when theirdiameters are increased during compression. All surfaces of every diskshould be well greased to facilitate relative motion between the diskand washers and between the disk and piston rods.

What has been shown and described therefor is a device which provides asimple and yet relatively inexpensive means of effectively attenuatingrecoil energy and reducing the peak force which exists in a mortarsystem. This has been accomplished by use of relatively few parts andassociated lower and reduced maintenance of the mortar system. Thisinvention has enabled the mortar to be mounted on a vehicle withoutdamage to the vehicle due to shock. It has enabled a mortar system to beutilized With a vehicle without an unacceptably high counterrecoil forceand accompanying oscillations. The use of the plastic resilient materialin any of the above described configurations as a dynamic forceattenuator is a new and novel concept.

Since it is obvious that many changes and modifications can be made inthe above described details without departing from the nature and spiritof the invention, it is to be understood that the invention is notlimited to said details except as set forth hereinafter.

What We claim is:

1. In a mortar, in combination,

a support housing,

a mortar tube mounted in said support housing,

volumetrically first and second compressible attenuation means mountedintermediate said mortar tube and said support housing for causing theforce of the counter-recoil to be substantially less than the force ofthe recoil of the mortar tube,

compressing means connected to said mortar tube for compressing saidattenuation means,

said first attenuating means being mounted adjacent a first means ofsaid compressing means and said second attenuating means being mountedadjacent an oppositely disposed means of said compressing means suchthat said first attenuating means reduces the peak recoil force and saidsecond attenuating means reduces the peak counter-recoil force;

and wherein said attenuating means comprises at least one layer ofcellular urethane elastomeric material which is compressible to a smallfraction of its free length under impact loads without substantialdeterioration.

2. In a mortor, in combination,

a mortar tube having first and second ends,

a tubular support member, radially inwardly protruding portions at itsoppositely disposed ends in which said mortar tube is rigidly mounted,

a radially outwardly protruding portion intermediate said oppositelydisposed ends,

a support housing in which said tubular support member is movablylocated therein,

a tubular receiving member mounted to one end of said support housingfor receiving a portion of said tubular support member,

a first and second plurality of layers of attenuating devices axiallydisposed on opposite sides of said radially outwardly protrudingportion,

said attenuating devices being composed of volumetrically compressiblecellular material having a density within the range of 0.3 to 0.6 gramper cubic centimeter, which reduces the peak force of recoil.

In a mortar, in combination,

support housing,

mortar tube,

tubular support member mounted in said support housing, volumetricallycompressible attenuation means mounted intermediate said mortar tube andwoog said support housing for causing the force of the counter-recoil tobe Substantially less than the force of the recoil of the mortar tube;

compressing means rigidly secured to said tubular support member, and

said motor tube being rigidly secured to said tubular support member,

said tubular support being movable relative to said support housing, and

said compressible attenuation means comprising first and second layersof volumetrically compressible ce1- lular structure mounted onoppositely disposed sides of said compressing means and surrounding saidtubular support member such that said rst layer attenuates the recoilforce and the second layer attenuates the counter-recoil force, and atubular end receiving member mounted on one end of said support housingand adapted to receive a portion of said tubular support member duringrecoil of said mortar.

References Cited UNITED STATES PATENTS BENJAMIN A. BORCHELT, PrimaryExaminer STEPHEN C. BENTLEY, Assistant Examiner U.S. Cl. X..R.

